Electric circuit



Oct. 10, 1944.

O. P. MCCARTY ELECTRIC CIRCUIT Filed Dec. 14, 1942 Inventor: Orin P. McCarty,

b Fw -7 y H s Attorney.

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*UNITED STATES PATENT ()FFICE ELECTRIC CIRCUIT Orin ll. McCarty, Pittsileld, Mass., assigrior to General Electric Company, a corporation-of New York Application December 14, 1942, Serial No. 468,923 9 Claims. (01. 171-119) This invention relates to electric circuits and more particularly to improvements in tap-changing-underload circuits.

When such circuits are used to control the ratio of a transformer they are known in the art as ioad-ratio-control circuits. One such circuit is described and claimed in my joint patent with Arthur Palme, No. 2,246,182, which is assigned to the assignee of the present application. In a sense this is a modification of the above-identified patent and one improvement comprises using the same insulating bushing which separates certain parts of the load-ratiocontrol equipment, which are inside-and outside of the transformer tank or housing respectively, as the insulator for one of the line terminals of the transformer. This is accomplished by so modifying the non-arcing duty switching mechanism of the equipment that there be no increase in the number of conductors running through the insulating bushing.

An object of the invention is to provide a new and improved electric circuit.

Another object of the invention is to provide a new and improved tap-changing-under-Ioad circuit.

Another object of the invention is to provide a new and improved load-ratio-control circuit Still another object of the invention is to provide an improved load-ratio-control circuit in which the same insulating bushing carries one of the line terminals and also carries some of the load-ratio-control switching equipment.

The invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

Referring now to the single figure of the drawing, I have illustrated schematically and diagrammatically therein an embodiment of the invention in which a main transformer l is mounted in an enclosing tank or housing 2. The transformer is provided with high voltage windin s 3 and 4 and with a low voltage tertiary winding 5. The high voltage windings may be connected as either an auto-transformer or as an insulating transformer and either winding may be the primary winding or the secondary winding. Winding 3 is provided with a plurality of taps 6 which are selectively engageable by a pair of ratio adjusters l and 8.

For performing the arcing duty of the equipment there is provided an arcing contactor 9 mounted on top of an insulating bushing I!) passing through a wall in the tank 2 and in this particular case it is the top of the tank. Also mounted on the bushing is a mainline terminal il forthe winding 3 to which a conductor !2 of a main circuit is connected.

For selecting the ratio adjuster whose current is to be interrupted by the arcing contactor there is provided a. non-arcing duty selector switch or switching means i3 which is shown mounted inside the transformer tank. As no appreciable arcing takes place at the contacts of the ratio adjusters l and 8 and at the contacts of the selector switch I3, these devices may be mounted under the surface of the clean cooling or insulating liquid which in the case of large high voltage transformers usually all but fills the transformer tank. The switching means i3 is essentially a polarity or connection reversing means but differs from the usual means of this type in that it has an intermediate position or condition in which both incoming and both outgoing conductors are all directly connected together. In other words, it has what amounts to a short circuiting intermediate position. This is for the purpose of preventing interruption of the load current when the selector switching means is moved from one end position to the other.

In order to prevent short circuiting of the winding 3 between any pair of adjacent taps a preventive reactor M in the form of a so-called split reactor is connected between the ratio adjusters and the selector switching means. This device consists of a pair of equal windings mounted on a common core, each winding being connected between one ratio adjuster and one of the poles of the selector switching means. The connections are such that the device has only leakage reactance with respect to load current which divides between its two windings but has magnetizing reactance with respect to circulating current which flows through its two windings.

The contactor 9 and the selector switching means I3 are electrically connected by a pair of.

conductors l5 and I6. These are preferably con.- centrically arranged so as to reduce to a minimum their reactance with respect to circulating current, that is to say, the current which flows up in one and down in the other, so as to reduce to a minimum any tendency for arcing to take place at the contacts of the selector switching means [3. The main line terminal II is permanently connected to the conductor l 6.

The ratio adjusters l and 8, the contactor 9 and the switching means 53 have a common reversible driving means shown as shafting ll and I8, bevel gearing I9, cams 2t, 2t and ratio adjuster mechanism 22. This means may be operated in any suitable manner, such as automatically, in response to voltage by means of a reversible motor 23 whose operation is controlled by a primary voltage control relay 26. Both the motor 23 and the relay 2d may be energized as shown, from the winding Th operation of the illustrated embodiment of the invention is as follows: The load-ratio control mechanism is shown in what is usually called the full cycle position in which both ratio adjusters make connection to the same tap and the selector switching means is shown in its in termediate position in which ratio adjusters d and 8 are connected to each other through. the windings or the reactor it and the contacts of the switching means it and are also connected to both of the concentric conductors l and it. All of the load current divides equally between th ratio adjusters, the windings of the reactor i l, and the contacts of the switching means l3; The load current divides inversely as the impedance of the circuits of the concentric conductors I5 and t6, the current through the tubular conductor i5 flowing through the closed arc ing contactor 9 and joining the current through the center conductor it. near the line terminal Assume now there is a change of voltage such that the relay 25 causes the motor 23 to turn the driving mechanism so as to cause the ratio adjusters to move counterclockwise, as viewed in the drawing. The first thing that happens is that the connection reversing switch 63 is moved to the left so that ratio adjuster 8 is connected to tubular conductor IE only and ratio adjuster l is connected to conductor it only. The result is that ratio adjuster 8 is now connected to the main line terminal through the arcing contactor 9, and ratio adjuster l is connected to the main line terminal through the conductor I6 and therefore not through the arcing contactor 9. The next thing that happens is that the arcin contactor 9 opens, thereby completely interrupting the current in the ratio adjuster 8 and causing all the load current to be carried'by the branch circuit which includes the ratio adjuster 1 and the conductor I6. The next thing that happens is that the ratio adjuster 8 moves counterclockwise until it makes contact with the adjacent tap. After this happens the arcing contactor 9 recloses. This does two things: The first is that it completes a. connection for load current to flow through the ratio adjuster 8, the tubular conductor IS, the arcing contactor 9 and out through the line terminal H. The second is that it completes a bridging connection between two adjacent taps whereby the voltage of the winding 3 between these taps circulates a current through the ratio adjusters, the arcing contactor and the rest of the branch circuits. The voltage of the line terminal ll now corresponds to the voltage substantially mid-way between the taps with which the ratio adjusters I and 8 make respective contact, whereas in the original full-cycle position, as illustrated in the drawing, the voltage of the line terminal H corresponded substantially to the voltage of the tap with which both ratio adjusters make contact.

However, in order to relieve contactor 9 of continuously carrying one half the load current in its other end position.

were

an' operating position of the ratio adjusters, the switch I3 is returned to itsillustrated interme: diate position immediately following the reclosure of contactor h.

If this change in voltage is not sufficient t satisfy the relay 2d, the motor 23 continues t operate and selector switch l3 moves from left to right from its intermediate bridging position in This, in effect, reverses the connections between the ratio adjustem l and 8 and the branch conductors l5 and I6 so that ratio adjuster l is now connected to the main line terminal through the arcing contactor and ratio adjuster 8 is connected directly to the main line-terminal H. The arcing contactor 9 then reopens, thus interrupting the current in the ratio adjuster '5 and this ratio adjuster then moves counterclockwise into contact with the same tap to which the ratio adjuster 8 has been moved. Arcing contactor 9 then recloses and selector switch it moves back to its bridging position, thus, in effect, completing one cycle of operation of the mechanism. This cycle may be repeated as many times as there are taps! It the motor 231 is reversed. in response to an opposite change in voltage applied to the control relay 24 the entire mechanism operates in the opposite order so that the ratio adjusters move clockwise, the adjuster ll preceding the adjuster 8 but only after the selector switching means I has connected. the adjuster which is to be moved 'in series with the arcing contactor and only after the arcing contactor has opened.

While there has been shown and described a particular embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the invention and, therefore, it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

i. In combination, a winding provided with a plurality of taps, a main circuit conductor for selective connection to said taps, a pair of ratio adjuster switches for selectively making contact with said taps, a pair of branch circuits connected respectively between said ratio adjuster switches and said main conductor, connection reversing means connected in said branch circuits between said ratio adjusters and said main circuit conductor, and an arcing contactor connected in one of said branch circuits between said reversing means and said main circuit conductor.

2. In combination, a' winding provided with a plurality of taps, a main circuit conductor for selective connection to said taps, a pair of ratio adjuster switches for selectively making contact with said taps, a pair of branch circuits conmenu, 1%!

selective connection to said taps, a pair of ratio adjuster switches for selectively making contact with said taps, a pair of branch circuits connected respectively between said ratio adjuster switches and said main conductor, connection reversing means connected in said branch circuits between said ratio adjuster switches and said main circuit conductor, and an arcing contactor connected in one of said branch circuits between said reversing means and said main circult conductor, said reversing means having an overlap during which both ratio adjuster switches are connected to both branch circuits.

4:, In combination, a transformer having a winding provided with a plurality of taps, a tank for enclosing said transformer, an insulating bushing passing through a wall of said tank, a iine terminal for said transformer mounted on the outer end of said bushing, an arcing contactor mounted on the outer end of said bushing, a pair of conductors extending lengthwise of the interior of said bushing, one of said conductors being permanently connected to said line terminal, the other of said conductors being connected to said line terminal through said arcing contactor, a pair of ratio adjusters in said tank for selectively making connection with said taps, and switching means having a normal position for connecting each ratio adjuster to both of said conductors, said switching means having two other positions in which each ratio adjuster is connected individually to a difierent one of said conductors but in reverse order respectively.

5. In combination, a transformer having a winding provided with a plurality of taps, a tank for enclosing said, transformer, an insulating bushing passing through a wall of said tank, a line terminal for said transformer mounted on the outer end of said bushing, an arcing contactor mounted on the outer end of said bushing, a pair of conductors extending lengthwise of the interior of said bushing, one of said conductors being permanently connected to said line terminal, the other of said conductors being connected to said line terminal through said arcing contactor, a pair of ratio adjusters in said tank for selectively making connection with said taps, switching means having a normal position for connecting each ratio adjuster to both of said conductors, said switching means having two other positions in which each ratio adjuster is connected individually to a different one of said conductors but in reverse order respectively, and a split reactor connected between said ratio adjusters and said switching means.

6. In combination, a transformer having a winding provided with a plurality of taps, a tank for enclosing said transformer, an insulating bushing passing through a wall of said tank, a line terminal for said transformer mounted on the outer end of said bushing, an arcing contactor mounted on the outer end of said bushing, a pair of conductors extending lengthwise of the interior of said bushing, one of said conductors being permanently connected to said line terminal, the other of said conductors being connected to said line terminal through said arcing contactor, a pair of ratio adjusters in said tank for selectively making connection with said taps, switching means having a normal position for connecting each ratio adjuster to both of said conductors, said switching means having two other positions in which each ratio adjuster is connected individually to a different one of said conductors but in reverse order respectively, a

split reactor connected between said ratio adjusters and said switching means, reversible driving means for operating saidswitching means in a cycle in which it goes between both of its other positions by way of its normal position,

means operated by said driving means for operating said contactor in a cycle in which it is open when said switching means is in either of said other positions and is closed whenever said switching means is in said normal position, and means operated by said driving means for moving said ratio adjusters alternately from tap to tap in whichever direction said driving means is operated, each ratio adjuster being moved only after said contactor has been opened and when it and said contactor are in series.

In combination, a transformer having a winding provided with a plurality of taps, a tank for enclosing said transformer, an insulating bushing passing through a wall of said tank, a line terminal for said transformer mounted on the outer end of said bushing, an arcing contactor mounted on the outer end of said bushing, a pair of concentric conductors extending lengthwise of the interior of said bushing, one of said conductors being permanently connected to said line terminal, the other of said conductors being connected to said line terminal through said areing contactor, a pair of ratio adjusters in said tank for selectively making connection with said taps, and switching means in said tank having a normal position for connecting each ratio adjuster to both of said conductors, said switching means having two other positions in which each ratio adjuster is connected individually to a different one of said conductors but in reverse order respectively.

8. In combination, a transformer having a winding provided with a plurality of taps, a tank for enclosing said transformer, an insulating bushing passing through a wall of said tank, a line terminal for said transformer mounted on the outer end of said bushing, an arcing contactor mounted on the outer end of said bushing, a pair of concentric conductors extending lengthwise of the interior of said bushing, one of said conductors being permanently connected to said line terminal, the other of said conductors being connected to said line terminal through said arcing contactor, a pair of ratio adjusters in said tank for selectively making connection with said taps, switching means in said tank having a normal position for connecting each ratio adjuster to both of said conductors, said switching means having two other positions in which each ratio adjuster is connected individually to a difierent one of said conductors but in reverse order respectively, and a split reactor connected be tween said ratio adjusters and said switching means.

9. In combination, a transformer having a winding provided with a plurality of taps, a tank for enclosing said transformer, an insulating bushing passing through a wall of said tank, a line terminal for said transformer mounted on the outer end of said bushing, an arcing contactor mounted on the outer end of said bushing, a pair of concentric conductors extending lengthwise of the interior of said bushing, one of said conductors being permanently connected to said line terminal, the other of said conductors being connected to said line terminal throughsaid arcnormal position for connecting each ratio adjuster to both. of said conductors, said switching 'means having two other positions in which each ratio adjuster is connected individually to a different one of said conductors but in reverse order respectively, a split reactor connected be tween said ratio adjusters and said switching means, reversible driving means ior operating said switching means in a cycle in which it goes between'both its other positions icy was of its normai position, means operated by said driv ing means for operating said contactor in a cycle in which it is open when said switching means is in either of-said. other positions and is closed whenever said switching means is in said normal position, and means operated by said driving means for moving saidratio adjusters alternately from tap to tap in whichever direction said driving means is operated, each ratio adjuster being moved only after said contactor has been opened iii and when it and said contactor are in series.

GRIN P. MCCARTY. 

